Impeller assemblies typically include an impeller housing which is mounted on or operably connected with a central drive shaft. Attached to the shaft, within the housing, is an impeller. The impeller typically includes upper and lower cover plates and a vane plate located between the respective cover plates. Fluid to be pumped is introduced into the impeller housing at one side thereof. The shaft rotates so as to rotate the impeller assembly thereby creating regions of high and low fluid pressure within the impeller housing and pumping fluid passing through the impeller assembly.
Depending on the application of the pump, a pump can be a single-stage model i.e. having one impeller assembly, or a multi-stage model i.e. having a number of impellers in series on the same shaft passing through each of the impeller housings.
In order to maintain the desired pressure levels within the impeller assembly, the fluid flow path through each of the impeller assemblies within the pump must be sealed. One conventional means of sealing the impeller housing against the drive shaft is to provide a caged annular seal, located radially between the impeller housing and the drive shaft. The seal ring is contained within a radial cavity and is provided with room to float radially to compensate for radial movement of the impeller relative to the impeller housing.
This type of seal has proven to be effective but suffers a number of disadvantages. Firstly, the floating seal is not free to float axially, meaning that any axial movement of the impeller relative to the impeller housing cannot be compensated for. Secondly, the seal is located within a groove formed in the impeller housing. Installation, as well as removal and replacement of the seal, is an intricate operation given the “hidden” location of the seal. Further, in order to provide an adequate seal, the sealing ring and drive shaft must be manufactured with very small tolerances in internal diameter so that it closely receives the drive shaft of the impeller assembly.
The above disadvantages are of course amplified when the pump is a multi-stage model.
It is therefore an object of the invention to provide a sealing arrangement for an impeller assembly that at least in part alleviates one or more of the above disadvantages.